Electro-optical device, driving method of electro-optical device, and electronic apparatus

ABSTRACT

A pixel circuit includes a driving transistor, a switching transistor, and a light emitting element, and the light emitting elements are formed on a semiconductor substrate. A first substrate potential is supplied to the switching transistor, and a second substrate potential, different from the first substrate potential, is supplied to the driving transistor.

BACKGROUND

1. Technical Field

The present invention relates to an electro-optical device thatintegrates a pixel circuit, for example, on a semiconductor substrate, adriving method of an electro-optical device, and an electronicapparatus.

2. Related Art

In recent years, a variety of electro-optical devices using a lightemitting element such as an organic light emitting diode (hereinafter,referred to as “OLED”) element, and the like have been proposed.Generally, in the electro-optical device, scan lines and data lines arewired on a glass substrate, and a pixel circuit is formed according tointersections of the scan lines and the data lines. In the pixelcircuit, apart from the light emitting element, a switching transistorturned on by selection of the scan lines, or a driving transistor forenabling a current according to holding potential to flow to the lightemitting element may be included. Since the pixel circuit is formed onthe glass substrate, the switching transistor or the driving transistorgenerally includes a thin-film transistor.

Meanwhile, in recent years, techniques for forming this kind of theelectro-optical device on a semiconductor substrate such as a siliconsubstrate is different from the glass substrate, have been proposed (Forexample, see U.S. Patent Application Publication No. 2007/0236440, andJP-A-2009-152113).

However, when forming the pixel circuit on the semiconductor substrate,problems are generated compared to a case of forming the pixel circuiton the glass substrate.

SUMMARY

An advantage of some aspects of the invention is to provide anelectro-optical device that considers problems generated when forming apixel circuit on a semiconductor substrate, a driving method of theelectro-optical device, and electronic apparatus.

According to an aspect of the invention, there is provided anelectro-optical device in which a scan line, a data line, and a pixelcircuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, a driving transistor that controls a current inaccordance with a potential of a gate node while being electricallyconnected to the first electrode of the light emitting element during aperiod when the current is supplied to the light emitting element, and aswitching transistor that is electrically connected between the gatenode of the driving transistor and the data line, wherein a firstsubstrate potential is supplied to the switching transistor, and whereina second substrate potential different from the first substratepotential is supplied to the driving transistor.

In the electro-optical device, when forming the pixel circuit includingthe switching transistor and the driving transistor on the semiconductorsubstrate, a substrate potential may be determined based on a rolerequired for each transistor. For this reason, it is possible tominimize effects of a leakage, or the like of the switching transistorcompared to a configuration in which the substrate potential simplycoincides with a source potential.

In the electro-optical device, when the switching transistor is anN-channel transistor, it is preferable that the first substratepotential be lower than a source potential of the switching transistor,and lower than a minimum value of the source potential.

Meanwhile, in the electro-optical device, when the switching transistoris a P-channel transistor, it is preferable that the first substratepotential be higher than a source potential of the switching transistor,and higher than a maximum value of the source potential.

According to another aspect of the invention, there is provided anelectro-optical device in which a scan line, a data line, and a pixelcircuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, an N-channel driving transistor that controls acurrent in accordance with a potential of a gate node while beingelectrically connected to the first electrode of the light emittingelement during a period when the current is supplied to the lightemitting element, and an N-channel switching transistor that iselectrically connected between the gate node of the driving transistorand the data line, wherein a first substrate potential is supplied tothe switching transistor, wherein a second substrate potential differentfrom the first substrate potential is supplied to the drivingtransistor, and wherein the first substrate potential is lower than thesecond substrate potential. In the electro-optical device, it ispossible to minimize effects of a leakage, or the like of the switchingtransistor.

According to still another aspect of the invention, there is provided anelectro-optical device in which a scan line, a data line, and a pixelcircuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, a P-channel driving transistor that controls a currentin accordance with a potential of a gate node while being electricallyconnected to the first electrode of the light emitting element during aperiod when the current is supplied to the light emitting element, and aP-channel switching transistor that is electrically connected betweenthe gate node of the driving transistor and the data line, wherein afirst substrate potential is supplied to the switching transistor,wherein a second substrate potential different from the first substratepotential is supplied to the driving transistor, and wherein the firstsubstrate potential is higher than the second substrate potential. Inthe electro-optical device, it is possible to minimize effects of aleakage, or the like of the switching transistor.

In the electro-optical device, the light emitting element and thedriving transistor may be connected in series between the firstpotential and the second potential, and the second substrate potentialmay be a common potential with a source node of the driving transistor.

In the electro-optical device, the pixel circuit may further include apower supply line for supplying the first potential, one of a sourcenode and a drain node of the driving transistor may be connected to thefirst electrode of the light emitting element so that the secondpotential different from the first potential is supplied to the secondelectrode of the light emitting element, the other of the source nodeand the drain node of the driving transistor may be connected to thepower supply line, and the first substrate potential may be lower thanthe second potential.

Here, the light emitting element and the driving transistor may beconnected in series between the first potential and the secondpotential, and the second substrate potential may be a common potentialwith one of the first potential and the second potential.

In the electro-optical device, the pixel circuit may further include apower supply line for supplying the first potential, one of a sourcenode and a drain node of the driving transistor may be connected to thefirst electrode of the light emitting element, the other of the sourcenode and the drain node of the driving transistor may be connected tothe power supply line, and a third substrate potential common with thefirst potential may be supplied to the driving transistor.

In the electro-optical device, the driving transistor may be obtained byconnecting, in series, at least two transistors to which a gate isconnected in common, and the second substrate potential may be suppliedto the at least two transistors. Here, even though a power supplyvoltage is increased, it is unnecessary to increase a withstand voltageof the transistor.

In the electro-optical device, one of a source node and a drain node ofthe switching transistor may be connected to the data line, and the gatenode of the switching transistor may be connected to the scan line.

In the electro-optical device, the pixel circuit may further include acapacitive element, and one of a source node and a drain node of theswitching transistor may be connected to an end of the capacitiveelement and the gate node of the driving transistor. Here, the currentflowing in the light emitting element may be a current according to avoltage held by the capacitive element. In addition, the current flowingin the light emitting element may be a current according to a voltagebetween a gate and a source of the driving transistor.

In the electro-optical device, the switching transistor may electricallyconnect the gate node of the driving transistor and the data line whenthe scan line is selected, and a scan line driving circuit for drivingthe scan line and a data line driving circuit for driving the data linemay be formed on the semiconductor substrate together with the pixelcircuit. Here, a separation well may be formed between a display unit inwhich the pixel circuit is provided and a peripheral circuit in whichthe scan line driving circuit and the data line driving circuit areprovided. In this manner, by forming the separation well, it is possibleto minimize the influences of an operation of the peripheral circuit onthe display unit.

In addition, the invention may be applied to a driving method of theelectro-optical device and electronic apparatus including theelectro-optical device, in addition to the electro-optical device. Astypical examples of the electronic apparatus, a display apparatus suchas a head mounted display, and an electronic viewfinder may be given.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating an electro-optical deviceaccording to an embodiment of the invention;

FIG. 2 is a plane view illustrating disposition of each component in anelectro-optical device;

FIG. 3 is a block diagram illustrating an electrical configuration of anelectro-optical device;

FIG. 4 is a view illustrating a well region in an electro-opticaldevice;

FIG. 5 is a view illustrating a pixel circuit in an electro-opticaldevice;

FIG. 6 is a view illustrating operation of an electro-optical device;

FIG. 7 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 8 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 9 is a view illustrating an operation of an electro-optical deviceaccording to application and modification examples;

FIG. 10 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 11 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 12 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 13 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 14 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 15 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 16 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 17 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 18 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 19 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 20 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 21 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 22 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 23 is a view illustrating a pixel circuit of an electro-opticaldevice according to application and modification examples;

FIG. 24 is a perspective view illustrating an HMD using anelectro-optical device according to an embodiment of the invention; and

FIG. 25 is a view illustrating an optical configuration of an HMD.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the accompanying drawings.

FIG. 1 is a perspective view illustrating an electro-optical device 1according to an embodiment of the invention.

The electro-optical device 1 shown in FIG. 1 includes a micro display 10which is applied to a head mounted display (HMD) to display an image.The micro display 10 is an organic EL device in which a plurality ofpixel circuits, a peripheral circuit for driving a corresponding pixelcircuit, and the like are formed on a semiconductor substraterepresented by a silicon substrate, and an OLED is included in the pixelcircuit. In addition, in the invention, a silicon substrate isillustrated as the semiconductor substrate, but a semiconductorsubstrate made of a material that is well known in the related art maybe applicable in the invention.

The micro display 10 is housed in a frame-like case 12 which is openedin a display unit, and is connected to an end of an FPC (FlexiblePrinted Circuit) substrate 14. A plurality of terminals 16 are providedin the other end of the FPC substrate 14, and are connected with acircuit module which is not shown. In addition, the circuit moduleconnected with the terminal 16 serves as a power circuit and a controlcircuit of the micro display 10 to feed a variety of potentials throughthe FPC substrate 14 and supply a data signal, a control signal, or thelike.

FIG. 2 is a plane view illustrating disposition of each component in theelectro-optical device 10, and FIG. 3 is a block diagram illustrating anelectrical configuration of the electro-optical device 10. In addition,in FIG. 2, for convenience of description, a state in which the case 12of FIG. 1 is removed is illustrated.

In FIG. 2, a display unit 100 is formed in an oblong rectangle in alateral direction, which is less than one inch of a diagonal when viewedin a plane. Specifically, in FIG. 3, in the display unit 100, scan lines112 in m rows are provided in a lateral direction in the figure, anddata lines 114 in n columns are provided in a vertical direction so asto keep mutual electrical insulation relation with each of the scanlines 112. The plurality of pixel circuits 110 are arranged in a matrixshape according to each of intersections of the scan lines 112 in m rowsand the data lines 114 in n columns.

Here, m and n are all natural numbers. In addition, for the sake ofconvenience to distinguish rows of a matrix of the scan lines 112 andthe pixel circuits 110, 1, 2, 3, . . . , (m−1), and m-th rows arereferred in this order from above in FIG. 3. In the similar manner, forthe sake of convenience to distinguish columns of a matrix of the datalines 114 and the pixel circuits 110, 1, 2, 3, . . . , (n−1), and n-thcolumns are referred in this order from the left in FIG. 3.

In addition, in practice, three pixel circuits 110 corresponding tointersections with the data lines 114 in three columns mutually adjacentto the scan lines 112 in the same rows represent one dot of a colorimage to be displayed, and correspond to each of pixels of R (red), G(Green), and B (Blue). In other words, in the present embodiment, aone-dot color is represented by additive color mixing of a lightemitting element of the three pixel circuits 110 of RGB.

In a periphery of the display unit 100, periphery circuits for drivingthe pixel circuits 110 are provided. The periphery circuit includes ascan line driving circuit 140 and a data line driving circuit 150, andthe scan line driving circuit 140 is provided on both sides of left andright with respect to the display unit 100. Specifically, as shown inFIG. 3, two scan line driving circuits 140 drive each of the scan lines112 in m lines from both sides.

The same control signal Ctry is supplied to each of the scan linedriving circuits 140 from the circuit module, and the same scanningsignals Gwr(1), Gwr(2), Gwr(3), . . . , Gwr(m−1), and Gwr(m) aresupplied to each of 1, 2, 3, (m−1), and m-th scan lines 112.

In addition, at the time of this supply, when delay of the scanningsignals does not cause a problem, only one scan line driving circuit 140may be provided on one side.

As shown in FIG. 2, the data line driving circuit 150 is providedbetween a connection location of the FPC substrate 14 and the displayunit 100. As shown in FIG. 3, an image signal Vd and a control signalCtrx are supplied from the circuit module to the data line drivingcircuit 150. The data line driving circuit 150 supplies the image signalVd to 1, 2, 3, . . . , (n−1), and n-th data lines 114 in accordance withthe control signal Ctrx, as the data signals Vd(1), Vd(2), . . . ,Vd(n−1), and Vd(n).

In addition, in the display unit 100, potentials V1 to V5 are suppliedto each of the pixel circuits 110 from the circuit module through theFPC substrate 14. In addition, in the present embodiment, among thepotentials V1 to V5, the potentials V1, V2, and V4 are supplied.

The pixel circuit 110, the scan line driving circuit 140, and the dataline driving circuit 150 are formed on a common silicon substrate. Amongthese, the scanning signals Gwr(1) to Gwr(m) which are output by thescan line driving circuit 140 are logic signals which are defined by Hor L level. For this reason, the scan line driving circuit 140 becomesan aggregate of CMOS logic circuits which are operated in accordancewith the control signal Ctry. In addition, the data signals Vd(1) toVd(n) which are output by the data line driving circuit 150 are analogsignals, but the data line driving circuit 150 sequentially supplies, to1 to n-th data lines 114, the data signal Vd supplied from the circuitmodule in accordance with the control signal Ctrx. For this reason, thedata line driving circuit 150 has also the CMOS logic circuit.Meanwhile, the pixel circuits 110 has a plurality of transistors whichwill be described below, and in the present embodiment, a P-channel typeand an N-channel type are mixed in the transistors.

For this reason, in the micro display 10 formed as the siliconsubstrate, a well region is formed as below.

FIG. 4 is a view illustrating a schematic disposition of a well regionin the micro display 10. When a P type is used as the silicon substrate,an N type well region (hereinafter, roughly referred to as “N well”) isformed as below.

That is, first, in a region where the display unit 100 is to be formed,an N well is formed along a plurality of belt-like opening portionextending in a transverse direction. Second, in a region where the scanline driving circuit 140 is to be formed, the N well is formed along aplurality of opening portions such as in the display unit 100 at almostthe same pitch. Third, in a region where the data line driving circuit150 is to be formed, the N well is formed on an upper side in FIG. 4,that is, on an opposite side of the display unit 100.

For this reason, consequentially, as shown the figure, in each of theopening portions in a region of the display unit 100 and a region of thescan line driving circuit 140, a P type well region (hereinafter,roughly referred to as “P well”) remains. For this reason, in an edgeportion between the region of the display unit 100 and the region of thescan line driving circuit 140, the N well is disposed in a frame shape,and the P well and the N well are alternately disposed inside the edgeportion. In addition, the frame shaped N well surrounding the displayunit 100 is separated from the N well facing the display unit 100 in theperipheral circuit by the P well.

Here, a width Wn1 of the N well in the display unit 100 and a width Wn2of the N well in the scan line driving circuit 140 are formed to beequal to each other. In the same manner, a width Wp1 of the P well inthe display unit 100 and a width Wp2 of the P well in the scan linedriving circuit 140 may be formed to be equal to each other.

In addition, as shown in FIG. 4, the P wells in seven lines are arrangedin each region of the display unit 100 and the scan line driving circuit140; however, in the present embodiment, the P well and the N welladjacent to each other correspond to one line, and therefore, the P welland the N well in m lines which is the number of lines of the pixelcircuits 110 are substantially disposed.

In addition, a blank portion in the figure is the P well when the P typeis used for the silicon substrate, but because this is not related tothe invention, the P well is shown as a blank.

FIG. 5 is a circuit diagram of the pixel circuit 110. In FIG. 5, thepixel circuits 110 for a total of four pixels of 2×2 according tointersections of the scan line 112 in i-th row and the scan line 112 in(i+1)-th row that is downwardly adjacent to the scan line 112 in i-throw, and the data line 114 in j-th column and the data line 114 in(j+1)-th column that is adjacent to the data line 114 in j-th column inthe right side are illustrated. Here, i and (i+1) are signs of generallyindicating lines in which the pixel circuits 110 are arranged, and arean integer ≧1 and ≦m. In the similar manner, j and (j+1) are signs ofgenerally indicating columns in which the pixel circuits 110 arearranged, and are an integer ≧1 and ≦n.

As shown in FIG. 5, each of the pixel circuits 110 includes an N-channelMOS (Metal Oxide Semiconductor) transistor 122, P-channel MOStransistors 124 and 126, a capacitive element 128, and an OLED 130 thatis a light emitting element. Each of the pixel circuits 110 has the sameconfiguration in an electrical manner, and therefore, the pixel circuit110 in i-th row and j-th column will be described as a representative.

The transistor 122 of the pixel circuit 110 in i-th row and j-th columnacts as a switching transistor, and a gate node is formed through aninsulating film on the P well of the silicon substrate although astructure of the transistor 122 is not particularly illustrated. Inaddition, two N-type diffusion layers are formed in a manner such thations are implanted using the gate node as a mask, and a source node anda drain node are formed in such a manner that each of the diffusionlayers are pulled out. In the transistor 122 having the above-describedconfiguration, the gate node is connected to the scan line 112 in i-throw, an end of the drain node or the source node is connected to thedata line 114 in j-th column, and the other end of the drain node or thesource node is connected to an end of the capacitive element 128 and acommon gate node of the transistors 124 and 126. In addition, apotential V4 is supplied to the P well of the transistor 122 through apower supply line 119. For this reason, a substrate potential of thetransistor 122 (a first substrate potential) becomes the potential V4.

In each of the transistors 124 and 126, a common gate node is formed ina common N well region of the silicon substrate through the insulatingfilm. In addition, in each of the regions corresponding to thetransistors 124 and 126, two P-type diffusion layers are formed in amanner such that ions are implanted using the common gate node as amask, and a source node and a drain node are formed in such a mannerthat each of the diffusion layers are pulled out.

Among these configurations, the source node of the transistor 124 isconnected to a power supply line 116 for supplying the potential V1 on ahigher position side of a power source together with the other end ofthe capacitive element 128, and the drain node of the transistor 124 isconnected to the source node of the transistor 126. The drain node ofthe transistor 126 is connected to an anode of the OLED 130. Inaddition, the potential V1 is supplied to a common N well region of thetransistors 124 and 126. For this reason, a substrate potential (asecond substrate potential) of the transistors 124 and 126 becomes thepotential V1.

In this manner, the transistors 124 and 126 connected in series act as asingle driving transistor. Specifically, the driving transistor uses thecommon gate node of the transistors 124 and 126 as a gate, the sourcenode of the transistor 124 as a source, the drain node of the transistor126 as a drain so that a holding voltage by the capacitive element 128,that is, a current according to a voltage between the gate and thesource flows to the OLED 130.

The anode of the OLED 130 is a pixel electrode (a first electrode) whichis individually provided for each of the pixel circuits 110. Meanwhile,a cathode of the OLED 130 is a common electrode 117 (a second electrode)over all of the pixel circuits 110, and a potential V2 on a lowerposition side of a power source is supplied to the cathode. The OLED 130is an element which includes the anode and the transparent cathodefacing each other on the silicon substrate and which interposes a lightemitting layer made of an organic EL material, and emits light withluminance according to a current flowing from the anode to the cathode.

In addition, in FIG. 5, each of Gwr(i) and Gwr(i+1) indicates a scanningsignal supplied to the scan lines 112 in i-th row and (i+1)-th row, andeach of Vd(j) and Vd(j+1) indicates a data signal supplied to the datalines 114 in j-th column and (j+1)-th column.

In addition, for convenience, in the pixel circuit 110 in i-th row andj-th column, the common gate node of the transistors 124 and 126 arerepresented as g(i, j).

Meanwhile, in regard to the capacitive element 128, capacity that isparasitic on the gate node of the transistors 124 and 126 may be used.

FIG. 6 is a view illustrating a display operation of the micro display10, and illustrates an example of a waveform of each of a scanningsignal and a data signal.

As shown in FIG. 6, scanning signals Gwr(1), Gwr(2), Gwr(3), . . . ,Gwr(m−1), and Gwr(m) are sequentially selected for each horizontalscanning period (H) over each frame by the scan line driving circuit 140to be exclusively in an H level. In addition, in the invention, theframe refers to a period required for displaying an image for one cut(frame) in the micro display 10. For example, when a vertical scanningfrequency is 60 Hz, the frame refers to a period of 16.67 millisecondsequivalent to one period of the frequency. In addition, in the scan linedriving circuit 140, a higher position side of a power source is apotential Vdd, and a lower position side thereof is a potential Vss. Forthis reason, in the scanning signals Gwr(1) to Gwr(m), an H levelcorresponds to the potential Vdd, and an L level corresponds to thepotential Vss.

When the scan line 112 in i-th row is selected, and the scanning signalGwr(i) is changed from the L level to the H level, in the data line 114in j-th column, a data signal Vd(j) of a potential corresponding to atarget value of luminance in i-th row and j-th column, that is, apotential corresponding to a driving current to flow to the OLED 130 issupplied to the data line 114 in j-th column by the data line drivingcircuit 150.

When the scanning signal Gwr(i) is in the H level in the pixel circuit110 in i-th row and j-th column, the transistor 122 is turned on, andtherefore, the gate node g(i, j) is electrically connected to the dataline 114 in j-th column. For this reason, a potential of the gate nodeg(i, j) becomes a potential of the data signal Vd(j) as shown by anarrow in FIG. 6. In this instance, the transistors 124 and 126 flow, tothe OLED 130, a current according to a difference in the potentialsbetween the gate node g(i, j) and the source node and a voltage betweenthe gate sources. In addition, the capacitive element 128 holds avoltage between the gate and the source in the transistors 124 and 126.

When the selection of the scan line 112 in i-th row is completed, andthe scanning signal Gwr(i) is in the L level, the transistor 122 isturned from on to off. A potential of each of the gate node of thetransistors 124 and 126 while a corresponding transistor 122 is in an onstate is kept by the capacitive element 128 even though the transistor122 is turned off. For this reason, even though the transistor 122 isturned off, the transistors 124 and 126 continuously flow, to the OLED130, a current according to a holding voltage by the capacitive element128 until the next scan line 112 in i-th row is repeatedly selected. Forthis reason, in the pixel circuit 110 in i-th row and j-th column, theOLED 130 continuously emits light over a period corresponding to oneframe with luminance according to a potential of the data signal Vd(j)when the i-th row is selected.

Here, since the transistors 124 and 126 are the P-channel, as thepotential of the data signal Vd(j) is on a lower position, the currentflowing in the OLED 130 is increased (luminance becomes brighter).

In addition, even in the pixel circuits 110 in i-th row other than inthe j-th column, the OLED 130 emits light with luminance according tothe potential of the data signal supplied to the corresponding data line114. In addition, the pixel circuit 110 corresponding to the scan line112 in i-th row has been described; however, the scan lines 112 areselected in the order of 1, 2, 3, . . . , (m−1), and m-th rows, andtherefore, each of the pixel circuits 110 emits light with luminanceaccording to each of target values. This operation is repeated for eachframe.

In addition, in FIG. 6, a scale of the potential of the data signalVd(j) and the gate node g(i, j) is enlarged than a potential scale ofthe scanning signal that is a logic signal for the sake of convenience.

However, in the pixel circuit 110, a role required for the transistor122 acting as the switching transistor and a role for the transistors124 and 126 acting as the driving transistor are different from eachother as follows. Specifically, the transistor 122 requires that offresistance is high, that is, an off-leakage is small, and a variationamount of the gate potential of the transistors 124 and 126 is reduced,whereas the transistors 124 and 126 requires that the current to flow tothe OLED 130 is stably supplied.

A substrate potential of the MOS transistor is generally configured soas to coincide with a source potential.

However, in the present embodiment, in order to reduce the off-leakageof the N-channel transistor 122, a substrate potential V4 of thetransistor 122 is set as being the same as or slightly lower than apotential of a minimum value of the source potential of the transistor122. Here, the substrate potential V4 of the transistor 122 is set asbeing the same as or slightly lower than the potential V2 on a lowerposition side of a power source. For this reason, the power supply line119 for supplying the potential V4 is provided separately from thecommon electrode 117 which is kept at the potential V2. In addition,when reducing the substrate potential, a threshold voltage becomeshigher, but in the present embodiment, priority is given to reducing theoff-leakage based on the role required for the transistor 122. Inaddition, in the N-channel transistor, when the substrate potential ishigher than the source potential, it is biased in the forward directiontoward the N diffusion layer from the P well, and therefore, anoperation failure occurs by the flow of a current.

Meanwhile, when the substrate potential of each of the P-channeltransistors 124 and 126 is higher than the source node, influences of anincrease in the threshold voltage cannot be ignored. In contrast, whenthe substrate potential is lower than the source node, an operationfailure may occur. For this reason, the substrate potential of each ofthe P-channel transistors 124 and 126 has to coincide with the potentialV1 of the source node.

Accordingly, in the present embodiment, the substrate potential of thetransistor 122 and the substrate potential of each of the transistors124 and 126 are appropriately set in accordance with each of therequired roles, and therefore, it is possible to reduce the leakage inthe transistor 122, and to stably supply the current to flow to the OLED130 by the transistors 124 and 126.

However, in order to enable the OLED 130 to emit light with luminance ofa certain degree, it is necessary to increase a power supply voltage,that is, a difference in the potentials V1 and V2. Meanwhile, as thecurrent flowing to the OLED 130 is reduced, a voltage between the anodeand the cathode (potential V2) of the OLED 130 is gradually reduced, anda voltage applied between the source and the drain of the drivingtransistor is gradually increased by that amount. Consequently, in astate in which the luminance of the OLED 130 is zero, the voltageapplied between the source and the drain of the driving transistorbecomes a maximum.

Here, in order to increase a voltage (withstand voltage) which can beapplied between the source and the drain of the transistor formed on thesilicon substrate, it is necessary to increase a size of the transistorto thereby reduce electric field density. However, when miniaturizationof the display unit 100 or high definition display is required, the sizeof the transistor is inevitably reduced, and therefore, the withstandvoltage is reduced. For this reason, in a configuration in which thenumber of driving transistors is 1, when making the OLED 130 emit lightwith low luminance, destruction may occur due to a voltage exceeding thelowered withstand voltage.

In other words, in the related art, there was a trade-off relationshipbetween making the OLED 130 emit light with high luminance by increasingthe power supply voltage, and the miniaturization of the display unitand the high definition display.

In this regard, in the present embodiment, a configuration in which thedriving transistor is connected in series by two transistors 124 and126. In this configuration, when the current does not flow to the OLED130, the transistors 124 and 126 are turned off, so that the drain nodeof the transistor 124 and the source node of the transistor 126 are in afloating state. For this reason, the voltage is not applied between thesource and the drain of the transistors 124 and 126. In addition, whenan amount of the current flowing to the OLED 130 is reduced, arelatively high voltage is applied between the source node of thetransistor 124 and the drain node of the transistor 126, but consideringthe voltage is divided into transistors 124 and 126, the high voltage isnot applied.

Accordingly, it is unnecessary to increase the withstand voltage of thetransistors 124 and 126.

As a result, in the present embodiment, by making the OLED 130 emitlight with high luminance, both the miniaturization of the display unitand the high definition display may be achieved.

In addition, when making the OLED 130 emit light with high luminance orone of the miniaturization of the display unit and the high definitiondisplay is required, a single driving transistor may be provided.

In addition, in the present embodiment, the frame-like N wellsurrounding the display unit 100 is separated from the N well facing thedisplay unit 100 in the peripheral circuit by the P well positioned aboundary portion. For this reason, the N well in the display unit 100and the P well surrounded by the N well have difficulty in receivinginterference due to operations of the scan line driving circuit 140 andthe data line driving circuit 150 which are the peripheral circuits. Inother words, since a local operation is constantly in progress by aclock or the like in the peripheral circuit, the peripheral circuit isthe source of noise, but has a structure having difficulty in exertinginfluences of the corresponding noise on the display unit 100, by the Pwell provided in the boundary portion.

In the present embodiment, widths Wn1 and Wn2 of the N well are thesame, and widths Wp1 and Wp2 of the P well are the same, and therefore,it is possible to simplify a process of forming the wells.

Application and Modification Example

The invention is not limited to the above-described embodiments, and avariety of application and modification examples which will be describedbelow may be possible. In addition, it is possible to appropriatelycombine one or a plurality of application and modification exampleswhich are arbitrarily selected.

Disposition of Well Region

In the present embodiment, as particularly shown in FIG. 5, the P welland the N well of the display unit 100 are formed for each row along arow direction, but the invention is not limited thereto. For example,the P well and the N well may be formed along a column direction.

In addition, different from each row, as shown in FIG. 7, each of thewells is alternately shared in an odd row and an even row adjacent toeach other. In this manner, when each of the wells is alternatelyshared, the power supply line 116 is shared in, for example, i-th rowand (i+1)-th row, and the power supply line 119 may be also shared in(i+1)-th row and (i+2)-th row which is not shown. Therefore, it ispossible to easily achieve pitch narrowing. Channel Type of Transistor

In the present embodiment, the N-channel transistor 122 is used as theswitching transistor, and the P-channel transistors 124 and 126 are usedas the driving transistor; however, the invention is not limitedthereto. Therefore, in the following description, a variety of variationof channels of the switching transistor and the driving transistor willbe described.

In FIG. 8, a configuration in which the P-channel transistor 122 and asingle N-channel transistor 125 as the driving transistor are provided,and a potential V5 is supplied to the other end of the capacitiveelement 128 is illustrated.

When the N-channel driving transistor is provided, the potential of thedata signal Vd(j) becomes a higher position, the current flowing to theOLED 130 is increased (luminance becomes brighter). For this reason, inthe configuration shown in FIG. 8, in order to reduce the off-leakage ofthe P-channel transistor 122, it is preferable that the substratepotential V4 of the transistor 122 be set as being a slightly highervalue than a potential of a maximum value of the source potential of thetransistor 122. Here, the substrate potential V4 of the transistor 122may be set as being a slightly higher value than the potential V1 on thehigher position side of the power source.

In addition, taking suppressing an operation failure with respect to thesubstrate potential V3 of the N-channel transistor 125 into account, itis preferable that the substrate potential V4 of the transistor 122 beset as being a minimum value (V2+Voled_th) of the source node, that is,less than a potential (V2+Voled_th) in which a luminescence thresholdvoltage Voled_th of the OLED 130 is added to a cathode potential V2 ofthe OLED 130.

In addition, when the P-channel transistor 122 is provided, thetransistor 122 is turned on in the L level, so that the scanning signalsGwr(1), Gwr(2), Gwr(3), . . . , Gwr(m−1), and Gwr(m) are sequentiallyselected for each horizontal scanning period (H) as shown in FIG. 9, andare exclusively in the L level.

In FIG. 10, the N-channel transistor 125 in FIG. 8 is serialized in thetransistors 124 and 126 of the same channel. Each of the substratepotentials V3 and V4 has the same configuration as that of FIG. 8.

In FIG. 11, the other end of the capacitive element 128 in FIG. 8 isconnected to the source node of the transistor 125, and power supplyingof the potential V5 is omitted. Each of the substrate potential V3 andV4 has the same configuration as that of FIG. 8.

In FIG. 12, the substrate potential of the transistor 125 in FIG. 8 isused as the source potential of the transistor 125, and power supplyingof the potential V3 is omitted.

In FIG. 13, the substrate potential of the transistor 125 in FIG. 11 isused as the source potential of the transistor 125, or the other end ofthe capacitive element 128 in FIG. 12 is connected to the source node ofthe transistor 125. In other words, in a configuration of FIG. 13, powersupplying of the potentials V3 and V5 is omitted compared to aconfiguration of FIG. 8.

In FIG. 14, the P-channel transistors 122 and 125 are illustrated. In aconfiguration of the P-channel transistors 122 and 125, only the N wellmay be formed in the display unit 100 of the silicon substrate.

When the P-channel transistor 122 is provided, it is preferable that thesubstrate potential V4 of the transistor 122 be set as being a slightlyhigher value than a potential of a maximum value of the source potentialof the transistor 122 as described above. Here, each transistorgenerally included in the pixel circuit 110 is operated within the samevoltage range. For this reason, the transistor 122 and the transistor125 may be set to have the same substrate potential, and therefore, thesubstrate potential V4 of the transistor 122 and the substrate potentialV3 of the transistor 125 may be the same potential. In the presentembodiment, the transistor 122 requires smaller off-leakage than that ofthe transistor 125, so that the substrate potential V4 may be set higherthan the substrate potential V3. In addition, the P-channel transistor125 is provided, the substrate potential V3 of the transistor 125 may beset as being larger than the potential V1 of the source node.

In addition, the substrate potential V4 of the transistor 122 and thesubstantial potential V3 of the transistor 125 may be common.

In FIG. 15, the P-channel transistor 125 in FIG. 14 is serialized in thesame channel transistors 124 and 126. Each of the substrate potentialsV3 and V4 has the same configuration as that of FIG. 14.

In FIG. 16, the other end of the capacitive element 128 in FIG. 14 isconnected to the source node of the transistor 125, and power supplyingof the potential V5 is omitted. Each of the substrate potentials V3 andV4 has the same configuration as that of FIG. 14.

In FIG. 17, the substrate potential of the transistor 125 in FIG. 14 isused as the potential V1 of the power supply line 116 connected to thesource potential of the transistor 125, and power supplying of thepotential V3 is omitted.

In FIG. 18, the other end of the capacitive element 128 in FIG. 17 isconnected to the source node of the transistor 125, and power supplyingof the potential V5 in addition to the potential V3 is omitted.

In FIG. 19, the N-channel transistors 122 and 125 are provided. In aconfiguration of the N-channel transistors 122 and 125, when the siliconsubstrate is a P type, the silicon substrate may be used as the P wellas is. It is preferable that the substrate potential V4 of the N-channeltransistor 122 be the same as or slightly lower than the sourcepotential of the transistor 122 as described above. Here, eachtransistor generally included in the pixel circuit 110 is operatedwithin the same voltage range. For this reason, the transistor 122 andthe transistor 125 may be set to have the same substrate potential, andtherefore, the substrate potential V4 of the transistor 122 and thesubstrate potential V3 of the transistor 125 may be the same potential.In the present embodiment, the transistor 122 requires smalleroff-leakage than that of the transistor 125, so that the substratepotential V4 may be set as being lower than the substrate potential V3.In addition, the substrate potential V3 of the N-channel transistor 125may be set as being less than (V2+Voled_th) as described above.

In addition, the substrate potential V4 of the transistor 122 and thesubstantial potential V3 of the transistor 125 may be common.

In FIG. 20, the N-channel transistor 125 in FIG. 19 is serialized in thesame channel transistors 124 and 126. Each of the substrate potentialsV3 and V4 has the same configuration as that of FIG. 19.

In FIG. 21, the other end of the capacitive element 128 in FIG. 19 isconnected to the source node of the transistor 125, and power supplyingof the potential V5 is omitted. Each of the substrate potentials V3 andV4 has the same configuration as that of FIG. 19.

In FIG. 22, the substrate potential of the transistor 125 in FIG. 19 isused as the source potential of the transistor 125, and power supplyingof the potential V3 is omitted.

In FIG. 23, the substrate potential of the transistor 125 in FIG. 21 isused as the source potential of the transistor 125, or the other end ofthe capacitive element 128 in FIG. 22 is connected to the source node ofthe transistor 125. In a configuration of FIG. 23, power supplying ofthe potentials V3 and V5 is omitted compared to the configuration ofFIG. 19.

The Others

In the embodiments, the substrate potential of each of the transistors124 and 126 are supplied by the power supply line 116, but may besupplied by a separate power supply line.

In addition, as the light emitting element, elements other than the OLEDmay be used. For example, an inorganic light emitting diode (LED) may beused. In addition, in a case in which the driving transistor isconnected in series, at least three light emitting elements may be used.

Electronic Apparatus

Next, a head mounted display adopting the micro display 10 according tothe embodiments will be described.

FIG. 24 is a diagram illustrating an appearance of a head mounteddisplay, and FIG. 25 is a diagram illustrating an optical configurationof the head mounted display.

First, as shown in FIG. 24, a head mounted display 300 includes a temple31, a bridge 32, and lenses 301L and 301R in appearance. In addition, asshown in FIG. 25, in the head mounted display 300, a micro display 10Lfor a left eye and a micro display 10R for a right eye are provided inthe vicinity of the bridge 32 and on the interior side (a lower side inthe figure) of the lenses 301L and 301R.

An image display surface of the micro display 10L is disposed so as tobe on the left side in FIG. 25. Due to this, a display image by themicro display 10L is emitted in the direction of 9 o'clock in the figurethrough an optical lens 302L. A half mirror 303L reflects the displayimage by the micro display 10L in the direction of 6 o'clock, andtransmits light incident from the direction of 12 o'clock.

The image display surface of the micro display 10R is disposed so as tobe on the right side opposite to the micro display 10L. Due to this, thedisplay image by the micro display 10R is emitted in the direction of 3o'clock in the figure through the optical lens 302R. A half mirror 303Rreflects the display image by the micro display 10R in the direction of6 o'clock, and transmits light incident from the direction of 12o'clock.

In this configuration, a wearer of the head mounted display 300 may seethe display images by the micro displays 10L and 10R in a see-throughcondition in which the display images are superimposed on an externalvideo.

In addition, in the head mounted display 300, when a left-eye image ofboth-eye images accompanying different parallaxes is displayed on themicro display 10L, and a right-eye image is display on the micro display10R, the display images may be perceived by the wearer as if the displayimages have a sense of depth or a three-dimensional effect (3D display).

In addition, the micro display 10 may be applicable as an electronicviewfinder in a video camera, a lens replacement type digital camera,and the like other than the head mounted display 300.

The entire disclosure of Japanese Patent Application No. 2011-166576,filed Jul. 29, 2011 and 2012-104847, filed May 1, 2012 are expresslyincorporated by reference herein.

1. An electro-optical device in which a scan line, a data line, and apixel circuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, a driving transistor that controls a current inaccordance with a potential of a gate node while being electricallyconnected to the first electrode of the light emitting element during aperiod when the current is supplied to the light emitting element, and aswitching transistor that is electrically connected between the gatenode of the driving transistor and the data line, wherein a firstsubstrate potential is supplied to the switching transistor, and whereina second substrate potential, different from the first substratepotential, is supplied to the driving transistor.
 2. The electro-opticaldevice according to claim 1, wherein the switching transistor is anN-channel transistor, and wherein the first substrate potential is lowerthan a source potential of the switching transistor.
 3. Theelectro-optical device according to claim 1, wherein the switchingtransistor is an N-channel transistor, and wherein the first substratepotential is lower than a minimum value of a source potential of theswitching transistor.
 4. The electro-optical device according to claim1, wherein the switching transistor is a P-channel transistor, andwherein the first substrate potential is higher than a source potentialof the switching transistor.
 5. The electro-optical device according toclaim 1, wherein the switching transistor is a P-channel transistor, andwherein the first substrate potential is higher than a maximum value ofa source potential of the switching transistor.
 6. An electro-opticaldevice in which a scan line, a data line, and a pixel circuit are formedon a semiconductor substrate, wherein the pixel circuit includes a lightemitting element having a first electrode and a second electrode, anN-channel driving transistor that controls a current in accordance witha potential of a gate node while being electrically connected to thefirst electrode of the light emitting element during a period when thecurrent is supplied to the light emitting element, and an N-channelswitching transistor that is electrically connected between the gatenode of the driving transistor and the data line, wherein a firstsubstrate potential is supplied to the switching transistor, wherein asecond substrate potential different from the first substrate potentialis supplied to the driving transistor, and wherein the first substratepotential is lower than the second substrate potential.
 7. Anelectro-optical device in which a scan line, a data line, and a pixelcircuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, a P-channel driving transistor that controls a currentin accordance with a potential of a gate node while being electricallyconnected to the first electrode of the light emitting element during aperiod when the current is supplied to the light emitting element, and aP-channel switching transistor that is electrically connected betweenthe gate node of the driving transistor and the data line, wherein afirst substrate potential is supplied to the switching transistor,wherein a second substrate potential different from the first substratepotential is supplied to the driving transistor, and wherein the firstsubstrate potential is higher than the second substrate potential. 8.The electro-optical device according to claim 6, wherein the lightemitting element and the driving transistor are connected in seriesbetween the first potential and the second potential, and the secondsubstrate potential is a common potential with a source node of thedriving transistor.
 9. The electro-optical device according to claim 1,wherein the pixel circuit further includes a power supply line forsupplying the first potential, wherein one of a source node and a drainnode of the driving transistor is connected to the first electrode ofthe light emitting element, wherein the other of the source node and thedrain node of the driving transistor is connected to the power supplyline, and wherein a third substrate potential common with the firstpotential is supplied to the driving transistor.
 10. The electro-opticaldevice according to claim 1, wherein the driving transistor is obtainedby connecting, in series, at least two transistors to which a gate isconnected in common, and wherein the second substrate potential issupplied to the at least two transistors.
 11. The electro-optical deviceaccording to claim 1, wherein one of a source node and a drain node ofthe switching transistor is connected to the data line, and wherein thegate node of the switching transistor is connected to the scan line. 12.The electro-optical device according to claim 1, wherein the pixelcircuit further includes a capacitive element, and wherein one of asource node and a drain node of the switching transistor is connected toan end of the capacitive element and the gate node of the drivingtransistor.
 13. The electro-optical device according to claim 12,wherein the current flowing in the light emitting element is a currentaccording to a voltage held by the capacitive element.
 14. Theelectro-optical device according to claim 1, wherein the current flowingin the light emitting element is a current according to a voltagebetween a gate and a source of the driving transistor.
 15. Theelectro-optical device according to claim 1, wherein the switchingtransistor electrically connects the gate node of the driving transistorand the data line when the scan line is selected, and wherein a scanline driving circuit for driving the scan line and a data line drivingcircuit for driving the data line are formed on the semiconductorsubstrate together with the pixel circuit.
 16. The electro-opticaldevice according to claim 15, wherein a separation well is formedbetween a display unit in which the pixel circuit is provided and aperipheral circuit in which the scan line driving circuit and the dataline driving circuit are provided.
 17. A driving method of anelectro-optical device in which a scan line, a data line, and a pixelcircuit are formed on a semiconductor substrate, wherein the pixelcircuit includes a light emitting element having a first electrode and asecond electrode, a driving transistor that controls a current flowingin the light emitting element while being connected to the firstelectrode of the light emitting element, and a switching transistor thatis connected between the gate node of the driving transistor and thedata line, the method comprising: supplying a first substrate potentialas a substrate potential of the switching transistor; and supplying asecond substrate potential different from the first substrate potential,as a substrate potential of the driving transistor.
 18. An electronicapparatus including the electro-optical device according to any one ofclaim
 1. 19. An electronic apparatus including the electro-opticaldevice according to any one of claim
 2. 20. An electronic apparatusincluding the electro-optical device according to any one of claim 3.